Control data determination from primary-side sensing of a secondary-side voltage in a switching power converter

Patent metadata

Field	Value
Publication number	US-9313840-B2
Application number	US-201213486625-A
Country	US
Kind code	B2
Filing date	Jun 1, 2012
Priority date	Jun 3, 2011
Publication date	Apr 12, 2016
Grant date	Apr 12, 2016

Abstract

A power distribution system includes controller of a switching power converter to control the switching power converter and determine one or more switching power converter control parameters. In at least one embodiment, the controller determines the one or more switching power converter control parameters using a resonant period factor from a reflected secondary-side voltage and an occurrence of an approximate zero voltage crossing of the secondary-side voltage during a resonant period of the secondary-side voltage. In at least one embodiment, the switching power converter control parameters include (i) an estimated time of a minimum value of the secondary-side voltage during the resonant period and (ii) an estimated time at which a current in the secondary-side of the transformer decayed to approximately zero.

First claim

What is claimed is:

1. A method comprising:
operating a switching power converter in discontinuous conduction mode when an input voltage to the switching power converter is less than a threshold voltage;
operating the switching power converter in critical conduction mode when the input voltage is greater than the threshold voltage;
receiving a primary-side sense signal, wherein the primary-side sense signal is from a portion of a switching power converter that includes a primary-side of a transformer and the sense signal represents a secondary-side voltage across a secondary-side of the transformer;
when the switching power converter is operating in critical conduction mode:
determining one or more times between approximately zero crossings of the secondary-side voltage during one or more resonant periods of the secondary-side voltage, wherein each resonant period occurs after the secondary-side voltage decreases to zero and before a current in the primary-side of the transformer increases from approximately zero;
determining one or more resonant period factors using the one or more times between approximately zero crossings of the secondary-side voltage;
determining a time value that indicates when an approximate minimum value of the secondary-side voltage occurs during at least one of the resonant periods using (i) the one or more resonant period factors and (ii) an occurrence of an approximate zero voltage crossing of the secondary-side voltage during a resonant period of the secondary-side voltage; and

generating a switch control signal pulse in accordance with the determined time value, which indicates occurrence of the minimum value of the secondary-side voltage, to control conductivity of a switch that controls current in the primary-side of the transformer of the switching power converter.

2. The method of claim 1 wherein the one or more switching power converter control parameters comprise an estimated time at which a current in the secondary-side of the transformer decayed to approximately zero.

3. The method of claim 2 wherein the one or more resonant period factors comprise a time that equals approximately one-fourth of the resonant period, and determining one or more switching power converter control parameters further comprises:
during a cycle of a switch controlling current in the primary-side of the transformer, subtracting the resonant period factor from a time of a first approximately zero voltage crossing of the resonant period to determine an estimated time at which a current in the secondary-side of the transformer decayed to approximately zero.

4. The method of claim 1 wherein the one or more switching power converter control parameters comprise an estimated time of a minimum value of the secondary-side voltage during the resonant period.

5. The method of claim 4 wherein the one or more resonant period factors comprise a time that equals approximately one-fourth of the resonant period, and determining one or more switching power converter control parameters further comprises:
during a cycle of a switch controlling current in the primary-side of the transformer, adding the resonant period factor to a time of a first approximately zero voltage crossing of the resonant period to determine an estimated time of a minimum value of the secondary-side voltage during the resonant period.

6. The method of claim 4 further comprising:
causing the switch controlling the current in the primary-side of the transformer to conduct one-quarter period after a detected zero voltage crossing of the secondary-side voltage.

7. The method of claim 1 wherein the one or more switching power converter control parameters comprise (i) an estimated time of a minimum value of the secondary-side voltage during the resonant period and (ii) an estimated time at which a current in the secondary-side of the transformer decayed to approximately zero.

8. The method of claim 1 wherein the signal representing the secondary-side voltage across a secondary-side of the transformer is a reflected secondary-side voltage across an auxiliary winding of the transformer coupled to the secondary-side of the transformer.

9. The method of claim 1 wherein:
determining each time between approximately zero crossings of the secondary-side voltage during one or more resonant periods of the secondary-side voltage comprises:
allowing the secondary-side voltage to resonate for at least one-half period between adjacent zero crossings; and

determining the one or more resonant period factors from the one or more times between approximately zero crossings of the secondary-side voltage comprises:
averaging times between multiple adjacent approximately zero crossings of the secondary-side voltage multiple at least one-half resonant periods to determine an average of the resonant period factors.

10. The method of claim 1 further comprising:
determining one or more times between approximately zero crossings of the secondary-side voltage during one or more resonant periods of the secondary-side voltage when an input voltage to the primary-side of the transformer is sufficient to reverse bias a body diode of a switch that controls current in the primary-side of the transformer.

11. The method of claim 1 further comprising:
detecting the approximately zero crossings of the secondary-side voltage.

12. The method of claim 1 further comprising:
generating a control signal to control power provided to a load.

13. The method of claim 12 wherein the load comprises one or more light emitting diodes.

14. An apparatus comprising:
a controller wherein the controller includes an input to receive a primary-side sense signal, wherein the primary-side sense signal is from a portion of a switching power converter that includes a primary-side of a transformer and the sense signal represents a secondary-side voltage across a secondary-side of the transformer, and during operation the controller is configured to:
determine one or more times between approximately zero crossings of the secondary-side voltage during one or more resonant periods of the secondary-side voltage, wherein each resonant period occurs after the secondary-side voltage decreases to zero and before a current in the primary-side of the transformer increases from approximately zero;
determine one or more resonant period factors using the one or more times between approximately zero crossings of the secondary-side voltage; and

determine a time value that indicates when an approximate minimum value of the secondary-side voltage occurs during at least one of the resonant periods using (i) the one or more resonant period factors and (ii) an occurrence of an approximate zero voltage crossing of the secondary-side voltage during a resonant period of the secondary-side voltage; and
generate a switch control signal pulse in accordance with the determined time value, which indicates occurrence of the minimum value of the secondary-side voltage, to control conductivity of a switch that controls current in the primary-side of the transformer of the switching power converter.

15. The apparatus of claim 14 wherein the one or more switching power converter control parameters comprise an estimated time at which a current in the secondary-side of the transformer decayed to approximately zero.

16. The apparatus of claim 15 wherein the one or more resonant period factors comprise a time that equals approximately one-fourth of the resonant period, and to determine the one or more switching power converter control parameters, the controller is further capable to:
during a

Assignees

• Grisamore Robert T
• He Zhaohui
• Cirrus Logic Inc

Inventors

• Grisamore Robert T
• He Zhaohui

Classifications

• H02M3/33523 Primary

  with galvanic isolation between input and output of both the power stage and the feedback loop · CPC title

• H05B33/0815 Primary

  Electricity · mapped topic

• Y02B20/346

  Cross-Sectional Technologies · mapped topic

• Y02B70/1433

  Cross-Sectional Technologies · mapped topic

• H05B45/3725

  Switched mode power supply [SMPS] · CPC title